<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .rectangle {
            position: relative;
            width: 200px;
            height: 100px;
            background-color: #ccc;
            border-radius: 0 0 10px 10px;
        }

        .half-circle {
            position: absolute;
            top: -50px;
            left: 0;
            width: 100px;
            height: 100px;
            background-color: #f00;
            border-radius: 50%;
            transform: rotate(180deg);
        }
        body{
            padding-top: 300px;
        }
    </style>
</head>

<body>
    <div class="rectangle">
        <div class="half-circle"></div>
    </div>

</body>

</html>